Evolutionary grade

Cladogram (family tree) of a biological group. The green box (central) may represent an evolutionary grade (paraphyletic), a group united by conservative anatomical and physiological traits rather than phylogeny. The flanking red and blue boxes are clades (i.e., complete monophyletic subtrees).

A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.[1]

  1. ^ Huxley J. 1959. Clades and grades. In Cain A.J. (ed) Function and taxonomic importance. Systematics Association, London.